Recently, there has been a considerable activity in the researches of boosted lean, a large-amount-of-EGR and homogeneous-charge self-ignition combustion of internal combustion engines for the purpose of reducing CO2 and emission. According to these researches, in order to maximize the results of CO2 reduction and emission reduction, it is necessary to realize a stable combustion state near the combustion limit. Also, petroleum fuel is being depleted, and robustness in stable combustion with a variety of fuel such as biofuel is required. The most important factor for realizing the stable combustion is to reduce differences in ignition of mixture and speedy combustion in which fuel is completely burned in the expansion stroke.
Also, a fuel supply of the internal combustion engine adopts an in-cylinder injection system in which fuel is injected directly in a combustion chamber for the purpose of improving the transient responsibility and the volume efficiency by evaporation latent heat and carrying out greatly retarded combustion for catalyst activation at low temperatures. However, the adoption of the in-cylinder injection system accelerates considerable oil dilution caused when spray fuel hits the wall of the combustion chamber as the spray fuel is in the form of liquid droplets and to considerable variations in combustion due to spray deterioration resulting from deposits grown around an injection aperture of the fuel valve with liquid fuel.
It is important to atomize the spray for realizing speedy evaporation of fuel in the combustion chamber in order to prepare for the oil dilution and the spray deterioration and to reduce the differences in ignition and realize stable combustion.
As ways to atomize the spray injected from the fuel injection valve, there are known an atomization by shearing force in a liquid film obtained in such a manner that the spray is formed into a thin film, an atomization by cavitation that occurs in removal of a flow, and an atomization of fuel deposited on a surface by mechanical vibrations of ultrasonic wave.
Patent Document 1 discloses a fuel injection valve in which the area of the cross section of a flow path in a bubble holding flow path is made larger than the cross section of a cavitation generating flow path, whereby the flow outlet of the cavitation generating flow path has a rapidly expanding flow. This fuel injection valve generates cavitation in the bubble holding flow path by designing the flow output of the cavitation generating flow path to have a rapidly expanding flow. As described above, various fuel injection valves that generate cavitation inside are proposed.